Method and a device for determination of the actual photosynthesis in plants

ABSTRACT

The invention relates to a novel method for simple and direct determination of the actual photosynthesis (the gross photosynthesis), the light respiration and the uptake and emission of CO2, O2 and H2O in connection with photosynthesis and respiration in plants. The invention also relates to a device for carrying out the method and use of the method for evaluation of the growth of algae and plants. The method of the invention is based on the new recognition that photosynthesis is not a chemical process but rather a one step physical reaction. The method is very different from the methods applied so far and much more accurate than these known methods. It has a great potential utility in agriculture and forestry. The method can be worked from great heights using aeroplanes or satellites. It can be used in all types of apparatuses, computers and computer programs designed for estimation of plant productivity and photosynthesis.

BACKGROUND OF THE INVENTION

The present invention relates to a method for the determination of theactual photosynthesis (the gross photosynthesis), the light respirationand the uptake and emission of CO₂, O₂ and H₂O in connection withphotosynthesis and respiration in plants. The invention also relates toa device for carrying out the method and use of the method forevaluation of the growth of algae and plants.

More specifically the invention relates to a method for determination ofthe actual photosynthesis (the gross photosynthesis) of plants, wherein:

-   -   the light photon flux falling on the photosynthetising surface        area of the leaves is measured and converted directly to the        amount of glucose produced per unit of the photosynthetising        area of the plant or the plant area per unit of time by means of        the conversion factor 1/36, as it requires 36 photons to produce        one molecule of glucose, and the absorption of the light photon        flux is related to the surface area of the plant. The actual        photosynthesis reaches a maximum at the optimal light photon        flux 1/6 μmole cm⁻² s⁻¹ for plants which do not have an        accessory carbon dioxide concentration mechanism (C₄ and CAM        plants), for the latter the actual photosynthesis continues to        follow the function 1/36 ×photon flux above the optimal photon        flux, ⅙ μmole cm⁻² s⁻¹,    -   the total actual photosynthesis of the plant, the plant part or        the plant area is calculated by multiplying the actual        photosynthesis by the size of the area, and optionally    -   the light respiration of plants is determined by multiplying the        actual photosynthesis by the conversion factor 5/6, as 5/6 of        the amount of CO₂ necessary for the actual photosynthesis is        produced by the light respiration.

The method according to the invention involves a simple and directmeasurement of the light photon flux falling on the photosynthesisingarea of the plant. The photon flux is converted to the produced amountof glucose/H₂O, CO₂, O₂ per unit of area per unit of time, and if adetermination of the actual photosynthesis (the gross photosynthesis),the net photosynthesis, the light respiration and the CO₂, O₂ and H₂Oconsumption/production for a plant unit, a whole plant or a plant areais desired, the rate per unit of area per unit of time found ismultiplied by the area belonging to the given photon flux.

The method of the invention is in principle very simple. But as theconversion factor between light and glucose production has never beendetermined with accuracy, it has not until now been possible todetermine the actual photosynthetic rate (plant gross production).

The net photosynthesis that previously has been determined as theexternal carbon dioxide uptake can now be determined by conversion ofthe photon flux. The invention is based upon the fact that adetermination of the internal carbon dioxide production called lightrespiration or photorespiration in plants has now become possible. Allthe processes of plants connected to photosynthesis, the actualphotosynthesis, the net photosynthesis, the light respiration and thecarbon dioxide, oxygen and water uptake and production connected tothese processes can now be determined by simple measurement of the lightphoton flux and the photosynthesising area of plants.

The method according to the invention and the use thereof is based on anovel approach to the concept of photosynthesis. This approach is verydifferent from the theories and models, which have been thought validfor the last century. The invention rests on the new recognition thatphotosynthesis is not a multi-step chemical reaction, but rather aphysical one-step process:

According to the new concept, the light photons are absorbed directly bya hexagonal constellation of carbon dioxide and water molecules, whichfunctions like a small electro motor. Each light photon exitates one ofthe 36 electrons of the 6 carbon atoms into circulation in the hexagonand thus binding the carbon dioxide molecules together with the watermolecules to the glucose hexagon. When 36 light photons have passedthrough the hexagon the glucose molecule has been formed. A physicalprocess (Fanger, A. M.: Dr. sci. (Dr. dr.) thesis, not yet submitted).

According to the previous theories, the light photons have been thoughtto be absorbed by chlorophyll and bound as electropotential energy,which via an electron transport chain was believed to lead to thechemical circular process called the Calvin cycle. In the Calvin cyclecarbon dioxide and water molecules have been considered as being builttogether via several chemical reactions to form the glucose molecule(Litterature: Gibbs, M.: “Structure and Function of Chloroplasts”,Springer Verlag, New York (1971); Hill, R. and Bendall, F: Function ofthe two cytochrome components in chloroplasts: a working hypo-thesis.Nature 186: 136-137 (1960); Calvin, M. and Bassham, J. A: “Thephotosynthesis of Carbon Compounds”. W. A. Benjamin, Inc., NewYork.(1962); Bassham, J. A., and Calvin, M.: The Path of Carbon inPhotosynthesis. Prentice-Hall Inc., Englewood. (1957)).

Prior Art

The photosynthetic process can be described by the equation:6CO₂+12H₂O+light photons-->C₆H₁₂O₆+6O₂+6H₂O

Each of the factors in the photosynthetic equation can be used—and hasbeen used—for the determination of the photosynthetic rate (moles ofglucose produced per unit of area or per unit of water flux volume (orweight) per unit of time). The problem has always been to separate thephotosynthetic activity from the respiration (the glycolysis), as therespiration can be seen as the opposite reaction of the photosynthesis:C₆H₁₂O₆+6O₂+6H₂O------>6 CO₂+12H₂O+energy

The only component, which separates the two processes, is the factorlight. But until now there has been controversy among experts as to howmany light photons are necessary for the formation of one mole ofglucose (Hopkins, W. G., Introduction to Plant Physiology, John Wiley &Sons (1999)). Furthermore it has not been known whether the plantpossibly functions like a prism and thus is able to upconcentrate light(Bjørn, L. O. and Vogelmann, T. C.: Quantifying Light andUltravioletRadiation in Plant Biology, Photochemistry and Photobiology64(3), 403-406 (1995)). It has until now not been possible to determineplant photosynthesis by light measurements. In one of the latest reviewson the subject of carbohydrate production (photosynthesis) John Farrarremarks: “A complete theory of photosynthetic regulation will thereforeintegrate the partitioning that underlies leaf area per plant with themechanisms which control density of photosynthetic machinery per unit ofarea of leaf. We do not have such a theory currently” (Farrar, J:Carbohydrate: Where does it come from, where does it go? In: Plantcarbohydrate biochemestry, ed. Bryant, John Allen, Oxford BiosScientific Publ. Environmental plant Biological series: p: 29-46 (1999).The previously applied methods have thus either measured the uptake ofcarbon dioxide, the emission of oxygen or the carbohydrate accumulation(harvest methods) as a measure for photosynthetic activity and/or growth(review see: Wittaker, R. H. Communities and Ecosystems, Mac MillanPublishing, New York (1975); Søndergaard, M. and Riemann, B.,Ferskvandsbiologiske Analysemetoder, Akademisk Forlag (1979); Nielsson,H. E., Remote sensing and image Analysis in Plant Pathology, Ann. Rev.of Plant Phytopathology 15, 489-527 (1995) and Buschmann, C. andLichtenthaler, H. K., Principles and Characteristics of Multicol orFluorescence Imaging of Plants, J. of Plant Physiol. 112, 297-314(1998)). The methods can be classified as follows:

1) Carbohydrate Accumulation (Determination of Length, Thickness andWeight):

The methods used here involve harvesting and drying of plant material,which is then converted to carbohydrate accumulated per unit of time.Thickness and height measurements are traditionally used in forestring(Wittaker, R. H., supra), but also in connection with weeds (Rosema, J.et al., Journal of Experimental vol. 38, nr. 188: 442-453 (1987)) andwith roots (Hackett, C., New Phythol. 68, 1023-1030 (1969)).

2) Carbon Dioxide:

a) The net exchange of carbon dioxide with the external air, measuredwith Infra Red Gas Analyser, where a determination of the carbon dioxidedifference between the ingoing and outgoing air of a plant measurementchamber gives a measurement of the net photosynthetic rate (Parkinson,K. J. and Legg, B. J., J. Phys. E. Sci. Instrum. 4, 598-600 (1971)). Asthis method of measurement does not separate photosynthesis andrespiration, the expression net photosynthesis is used. The method hasbeen much used for the last 25 years and is still much used. The methodis used in scientific experiments but is also of economic importance inthe evaluation of crop plant production in agriculture as well asforestry (see also: Long, S. P. and Woolhouse, H. W., J. Exp. Bot. 29:567-577 (1978); Fanger, A. M., The Influence of Nitrate and SodiumChloride on Growth, Photosynthesis, Root respiration and release of RootExudate of Spartina Anglica (C. E. Hubbard) elucidated by experiments inthe Laboratory, The University of Aarhus, Denmark (1982)).

-   -   b) Incorporation of the radioactive tracer C¹⁴, taken up as        C¹⁴O₂ or C¹⁴O₃, can be used for estimation of carbon dioxide in        plants (Fanger, A. M. (1982), supra) and is the standard        employed method for estimation of productivity of phytoplankton        (Søndergaard, M. and Riemann, B., (1979) supra).        3) Oxygen:

The productivity of higher plants as well as of phytoplankton can bemeasured by determination of oxygen either by titration or by means ofoxygen electrodes. The titration method has not been used as much as themeasurement of carbon dioxide as it is not as accurate (Søndergaard, M.and Riemann, B., supra).

4) Photosynthetic Enzymes:

A lot of experiments have been undertaken to examine whetherphotosynthetic enzymes can be used as a parameter for the photosyntheticrate (Cambell et al. (1988), Plant Phy-siol. 88, 1310-1316; Bowes, G.(1991), Plant cell and Environment 14, 795-806. Stitt, M. and Schulze,D. (1994), Plant Cell and Environment 17: 465-487. Harmens, H. et al.(2000), Physiologia Plantarum 108: 43-50).

5) Light:

A crude determination of plant covered areas can be undertaken fromaeroplanes or satellites (Nilsson, H. E., supra). Fluorescence methodshave also been developed recently, but so far they can only be used as ameasurement of diseases and as a measurement of chlorophyll (potentialphotosynthetic capacity) (Buschmann and Lichtenthaler (1998) supra).However, as mentionedpreviously it has not been known whether plants areable to concentrate light, and neither has the exact number of photonsnecessary for the formation of one molecule of glucose been known, sountil now light has not been a usable parameter for the estimation ofphotosynthetic rates.

SHORT DESCRIPTION OF THE METHOD OF THE INVENTION

Based upon the novel approach to the concept of photosynthesis it hasnow become possible to relate the light photon flux to the formation ofone molecule of glucose by simple multiplication by the factor 1/36,because:

-   a) it takes 36 photons to form one molecule of glucose.-   b) the factor light is related to the surface of the plant whereas    the factor carbon dioxide is related to the weight (or volume) of    the gross water flux related to photosynthesis;-   c) a steady and simple relationship exists between the actual    photosynthetic rate, the net photosynthetic rate and the light    respiration rate and-   d) the photosynthetic reaction is the fastest possible existing    organic reaction.

By the method of the invention it is therefore possible to determine 1)the actual photosynthetic rate, 2) the net photosynthetic rate, 3) thelight respiration rate, 4) the gross water flux rate and 5) the carbondioxide and oxygen uptake and emission rates in connection withphotosynthesis. Furthermore the actual velocity of the photosyntheticreaction has been computed by logic.

The method developed is characteristic by measurement of the lightphoton flux (photons, which can be used by plants for photosynthesis)combined with a measurement of the photosynthesising surface area of theplant connected to the measured light photon flux.

Determinations of the actual photosynthesis, the light respiration, thenet photosynthesis and the hereto connected water, carbon dioxide andoxygen uptakes and emissions according to the new method are carried outas follows:

The actual photosynthesis (the gross photosynthesis): The light photonflux is measured with one or more light sensors, which count lightphotons that can be used by plants for photosynthesis. The light photonflux is converted to moles of glucose produced by the plant part, theplant, plants, or plant area per unit of time, by multiplying the photonflux measured by the factor 1/36, as it takes 36 photons to form onemolecule of glucose. As it has been proved that the light flux isrelated to the surface area of the plant the plants, the actualphotosynthetic rate of a plant is the light photon flux per plantsurface area unit multiplied by the factor 1/36. The total actualphotosynthesis of the plant is determined by multiplying thephotosynthetic rate per surface area unit with the photosynthesisingsurface areas of the plant belonging to the measured photon fluxes. Theactual photosynthesis reaches a maximum at the optimal photon flux forphotosynthesis, 1/6 μmole cm⁻² s⁻¹, at which it grows constant at thevalue 1/6 μmmole cm⁻² s⁻¹. Measured light fluxes above the optimal lightflux, 1/6 μmole μmole cm⁻² s⁻¹ (1667 μmole m² s⁻¹) should be calculatedas being 1/6 μmole cm⁻² s⁻¹ for plants which do not possess an accessorycarbon dioxide concentration mechanism. For plants which do possess anaccessory carbon dioxide concentration mechanism, C₄ and CAM plants, theactual photosynthesis continues to follow the function 1/36× photon fluxabove the photon flux: 1/6 μmole μmole cm⁻² s⁻¹. Measurements should notbe made at light photon fluxes above those to which the plant has beenaccommodated during growth. That light is the growth limiting factor andthe actual photosynthesis follows the functions described above can beascertained by making a plot of photosynthesis measured as carbondioxide uptake as a function of light flux.

Light Respiration:

As the plant light respiration contributes with 5/6 of the carbondioxide necessary for the actual photosynthesis, while the netphotosynthesis with 1/6, it is now possible to determine the respirationof plants in light from the actual photosynthesis which is determined asdescribed above, by multiplication with the conversion factor 5/6.

The light respiration rate can also be determined by a combination ofthe method relying on lightphoton flux and area and the traditionalcarbon dioxide uptake method:

-   the light respiration rate per area unit per time unit is: 1/36    (F*_(CO2)−photon flux)

As the respiratory rate is an expression of carbon dioxide emitted byrespiration, the light respiration rate would most correctly beexpressed as carbon dioxide emitted per unit of water per unit of time.

The light respiration rate per unit of water per unit of time is: 1/216(1−F*_(CO2)/photon flux).

F_(CO2) is the carbon dioxide exchange per area unit, which can bemeasured by Infra Red Gas Analyser as described previously.

-   -   Air and water are connected to standard conditions for        comparisons.        Net Photosynthesis:

As the net photosynthesis is the expression for the external uptake ofcarbon dioxide necessary for the actual photosynthesis, whichconstitutes 1/6 of the actual photosynthesis, the net photosynthesis canbe determiined as follows:

The net photosynthesis is: the measured light photon flux multiplied bythe conversion factor 1/36 (=actual photosynthesis) times the factor1/6, times the areas of the plant photosynthesising surface connected tothe measured light photon flux. This result will be expressed in glucoseequivalents. Multiplied by the factor 6, the result will be in carbondioxide equivalents.

The Water Flux Rates:

The Gross Water Flux:

The gross water flux rate is the amount of water which according to thenew photosynthetic equation is connected to the actual (gross)photosynthetic rate and passing through the one square centimetre, towhich the actual photosynthesis per flux definition is connected. As ittakes 12H₂O molecules and 36 light photons per glucose molecule formed,

the gross water flux rate through 1 cm² can be determined as themeasured light photon flux per cm² multiplied with the conversion factor1/36 (mole glucose formed) times 12.

The gross water flux in moles is therefore equal to the measured photonflux per square centimetre times the conversion factor 1/3. The resultwill be in moles per cm² per s. If the result is desired in grams percm² per s: the gross water flux is 6 times the measured light photonflux, as the mole weight of water is 18 g.

Net Water Flux:

Half of the water molecules are, according to the photosyntheticequation, recirculated and the actual amount of water used for theactual photosynthesis will only be half of the gross water flux rate. Ifthe water flux for a plant part, a plant or a plant area is desired, themeasured photon fluxes should be multiplied with the plant surfaceareas, which are subjected to the light photon fluxes in question. Thewater fluxes connected to the net photosynthesis and the lightrespiration can be computed in the same manner in accordance with thephotosynthetic and glycolytic (respiratory) equations.

The Carbon Dioxide Fluxes:

The carbon dioxide fluxes connected to the actual photosynthesis and thelight respiration can now be calculated from a determination of theactual photosynthesis and light respiration by light photon flux andplant surface area as described above and the new photosyntheticequation where it takes 36 light photons to form a glucose molecule.

The Oxygen Fluxes:

The oxygen fluxes connected to the actual photosynthesis and the lightrespiration can now be determined from a determination of the actualphotosynthesis and light respiration by light photonflux and plantsurface area as described above and the new photosynthetic equationwhere it takes 36 light photons to form a glucose molecule.

When carbon dioxide is the growth limiting factor the rates will bedetermined by carbon dioxide. Carbon dioxide is related to water, to thegross water flux connected to the actual photosynthetic rate as thegross water flux is a function of the light photon flux as is the actualphotosynthesis, the net photosynthesis and the light respiration. Theconnected carbon dioxide and oxygen exchanges in accordance with the newphotosynthetic equation will therefore be constant when plant growth islimited by carbon dioxide.

The method of the invention can be universally employed for calculationof the actual photosynthesis (gross photosynthetic production) becauseit is very accurate and gives a quick and reliable estimate ofphotosynthesis wherever such an evaluation is necessary.

It is possible to compute the respiration of plants taking place inlight either from the difference between the actual photosynthesiscomputed on the basis of the light photon flux and the netphotosynthetic rate measured as carbon dioxide exchange or directly froma light photon flux measurement. It is absolutely novel that adetermination of the actual photosynthetic rate, the respiration rate inlight, and the gross water flux is possible. The method can replace thepreviously used carbon dioxide exchange, C¹⁴ and oxygen methods.

Moreover this new method gives the possibility of determinating theactual photosynthetic rate and the light respiration rate which has notbeen possible with the previous methods. The method can be workedeffortlessly from great heights using aeroplanes and satellites, as theonly measurements to be made are those of the light photon flux and thephotosynthesising area. The method can be used in all sorts ofapparatuses, computers and computer programs designed for estimation ofplant productivity and photosynthesis. A precise measurement of thelight photon flux over an area of soil over a period of time, forexample a year, can give an exact image of how large a harvest ispossible on the site in question. An accurate evaluation of whetherimprovement of plants, fertiliser or the like can bring an improvementof the harvest can be made by comparing the actual harvest with thepotential harvest estimated in this manner.

The invention further relates to a device for use in the above method,enabling a direct determination of the actual photosynthesis (the grossphotosynthesis) of plants by measuring the light photon flux falling onthe photosynthetising surface area of the leaves and converting saidflux to the specific amount of glucose produced per unit of thephotosynthetising area of the plant or the plant area per unit of time.The device according to the invention comprises a photon fluxmetercombined with an area meter and connected to a computer unit which,based on the measured photon flux and area, can calculate and read outthe total actual photosynthesis of the plant, the plant part or theplant area and, if desired, the light respiration, the water gross andnet flux, oxygen and carbon dioxide change of the plant area inquestion.

Methods:

Measurement conditions: Be certain to measure under conditions as closeto the natural conditions or the growth conditions as possible. Do notmeasure at light flux intensities larger than the ones to which theplants has been accommodated through growth, because theirphotosynthetic capacity may not be large enough to exploit the higherlight flux intensity. Under most conditions light will be the growthlimiting factor and the measurements can be computed in accordance withthe present method, based on light photon flux and area. However ifcarbon dioxide, water or other pure growth conditions are the limitingfactors, the actual photosynthetic rate, the net photosynthetic rate,the light respiration rate and other rates depending on these rates canbe expected to be constant from a certain light flux level. This can beascertained by producing a CO₂ exchange response curve to photon fluxdensity.

The photon flux at which the CO₂ exchange gets constant is the photonflux which should be used for the calculation of the different rates.When either carbon dioxide or water is the growth limiting factor, theconstant rates per unit of gross water flux should be used.

In general one can assume that light is the growth limiting factor up tothe optimal light photon flux for plants of 1667 Imole m−2 s−1; abovethis photon flux carbon dioxide is the growth limiting factor except forplants with extra carbon dioxide uptake mechanisms such as C4 and CAMplants, for which light also is the growth limiting factor above theoptimum light flux concentration.

A note on units: As flux is originally defined in centimetres, popularlyexpressed as the velocity of one cubic centimetre trough one squarecentimetre, comparisons of the different fluxes has to be made incentimetre units. This is important as the light flux is related to thesurface area and carbon dioxide is related to the water weight andthereby to the gross water flux in connection with the actualphotosynthesis of one square centimetre. The important relationship isthat the unitless value of 1 square centimetre=the unitless value of 1cubic centimetre=the unitless value of the weight of 1 cubic centimetreof water. All three values are equal to 1.

Determination of the Actual Photosynthetic Rate from Photon FluxMeasurement:

(a) Determination of Rate Per Surface Unit of Plant:

-   -   1) The light photon flux is measured on the photosynthesising        surface of the plant with a photon fluxmeter, which is designed        to register photons to be utilized by plants for photosynthesis,        for instance a photon fluxmeter from SKYE equipped with a PAR        sensor.    -   2) The photon flux measurement is repeated the desired number of        times and the average is calculated.    -   3) The actual photosynthetic rate is computed as:        actual photosynthetic rate=1/36× photon flux        (b) Measurement of a Whole Plant:    -   1) The photon flux is measured at different places on the plant        (from brightest to darkest) with a photon fluxmeter.    -   2) The areas corresponding to the given photon fluxes are        measured as well and noted. They can either be measured with an        areameter, for instance an areameter of the type LI-COR. 3000,        or the area can be determined by drawing the leaves on paper        which can be weighed and compared with the weight of 1 cm² or        100 cm² of paper or drawn on millimetre or other squared paper        where the squares can be counted.    -   3) The actual photosynthesis for the whole plant can thereafter        be calculated by multiplying the actual photosynthetic rate by        the areas belonging to the measured photon fluxes as outlined        above. All results are added, and the total actual        photosynthesis for the whole plant is thus calculated.        (c) 24 Hour Measurement:

If an estimate is desired for a 24 hour period, the photon fluxes aremeasured on the photosynthesising surfaces in repeated intervals, forinstance per hour. The areas are measured after finishing themeasurements if they have to be harvested. The calculation is carriedout as described above.

(d) Year Measurement:

If an estimate for a growth season or a year is desired, the photon fluxand the corresponding areas are measured for e.g. ten plants, forexample every other week. The average is calculated as described above.

All the different rates can then be calculated from the measured photonfluxes in accordance with the new photosynthetic equation:6CO₂+12H₂O+36 photons------>C₆H₁₂O₆+6H₂O+6O₂Large Scale Use of the Method According to the Invention:

For use in large scale working of the invention apparatuses, whichmeasure the light photon flux falling on the plant surface and at thesame time measure the surface areas of the plant corresponding to thelight flux, would be convenient. All the measured results should beintegrated by a computer to a total result for the whole plant, theplants or the plant areas after conversion of the measurements to actualphotosynthesis, light respiration, net photosynthesis and thecorresponding water, carbon dioxide and oxygen fluxes. The light fluxfor single plants should be measured at an angle perpendicular to theplant surface. The measurements can be made for small square units, forinstance per square millimetre, but should preferably be calculated persquare centimetre.

A device which simultaneously measures the light photon flux falling ondifferent places of the leaf and the plant surface areas belonging tothe measured photon fluxes may comprise a series of light sensors, whichmeasure photoquanta that can be used for photosynthesis, and which iscombined with an area measuring integrating stripe. The results are,e.g. by infra red rays, transferred to a computer where the results arecalculated and worked out to for instance: actual photosynthesis, lightrespiration, net photosynthesis, gross and net water flux and the carbondioxide and oxygen exchanges connected thereto.

For greater land areas the light photon flux falling perpendicular tothe soil surface should be measured and multiplied by the correspondingplant covered area, the assumption being that all light photons comingfrom the sun, falling on a leave mosaic, are absorbed as if the soil hadbeen covered by photosynthesising cloth. For example, small lightphotoquanta sensors, which are combined with a technique that is able tosend the results to planes or satellites, are placed or thrown out onthe place which is to be measured. From the satellite or plane thephotosynthesising plant areas in question are estimated, e.g. by infraread photographing. For area estimation of phytoplanctonic algae, aspecial method must be developed, for instance counting (flow cytometry)in combination with area evaluation of the phytoplanctonic algae. Anevaluation by photographic methods is also possible. For example, lightsensors are placed on a stick for measurement of light photoquanta,which can be used for photosynthesis by phytoplancton. The plancton isphotographed or collected at the corresponding depths for e.g.flowcytometry counting or in any other manner which will allow forsurface area estimation of the phyto plancton. Leaf-like algae(thallophytes) can be estimated with a water tight device like for landplant or large area measurement methods.

The invention is further illustrated by means of the following examples,which are not intended to limit the invention in any way.

EXAMPLES Example 1 Determination of the Actual Photosynthesis LightRespiration and Water Flux on a Leaf

Determination on leaf of evergreen laurie from Mar. 5, 2001, 11 a.m.,sunshine, air temperature: 2° C., Schleswig-Holstein, Germany.

The light photon flux was measured with a SKYE photon flux meterequipped with a PAR special sensor. The area of the leaf was in thisinsance drawn on millimeter squared paper and counted.

Measurements:

-   Photon flux on the leaf upside surface: 1490; 1486; 1484 μmole m⁻²    s⁻¹;-   Average=1487+/−3 μmole m⁻² s⁻¹.-   Photon flux on leaf downside surface 91; 86; 75 μmole m⁻² s⁻¹;-   Average=84+/−7 μmol e m⁻² s⁻¹.-   The leaf surface area was determined to: 15.9 cm²,-   The light photon flux: 1487 μmole m⁻² s⁻¹=0.1487 μmole cm²s⁻¹<1/6    (0.1667) μmole cm⁻² s⁻¹ and as the laurie has grown naturally and    thus is assumed accomodated to the light photon flux at which the    measurement takes place, light is assumed to be the growth limiting    factor and the calculations are as follows:    The Actual Photosynthesis of the Leaf:-   Leaf upside, the actual photosynthesis=1/36× photon flux×leaf    surface area:-   0.1487/36 μmole cm⁻² s⁻¹×15.9 cm²=0.06567 μmole s⁻¹.-   Leaf downside, the actual photosynthesis:-   0.0084/36 μmole cm⁻² s⁻¹×5.9 cm²=00.00366 μmole s⁻¹.-   Total leaf actual photosynthesis: 0.0693 μmole s⁻¹.

The Light Respiration of a Leaf_(area):

-   The total light respiration of the leaf=5/6× the actual    photosynthesis:-   15.9 cm²×(5/6×1/36×0.1487+5/6×1/36×0.0084) μmole cm ⁻² s⁻¹=0.0579    μmole s⁻¹.-   The net photosynthesis=The actual photosynthesis−light    respiration=0.0693 μmole s⁻¹−0.0579 μmole s⁻¹=0.0114 μmole s⁻¹.-   The gross water flux_(area) calculated from photonflux-   Gross water flux=6× photonflux×plant surface area:-   total gross water flux: 15.9.cm²×6 (0.1487+0.0084) gcm⁻² s⁻¹=7.5 g    s⁻¹.-   The net water flux=3× photon flux×leaf area:-   total net water flux: 15.9.cm²×3 (0.1487+0.0084) g cm⁻² s⁻¹=3.75 g    s⁻¹.-   The total water consumption of the leaf: gross=7.5 g s⁻¹; net=3.75 g    s⁻¹.

Example 2 Comparison of the New Method with the Carbon Dioxide ExchangeMethod and Comparison of Light Respiration with a Combination of LightFlux and Carbon Dioxide Exchange Determination

Data originate from an experiment with Spartina anglica, a C₄ marchgrass grown in a 1% sodium chloride nutrient culture (Fanger, 1982,supra). The calculations are based on average values. The calculation ofaverage values are omitted, as they are assumed known.

Measurements:

-   Light photon flux: 1900 μmole m⁻² s⁻=0.1900 μmole cm⁻² s⁻¹;-   measured with a photon flux meter, LI-COR LI-188, Quantum,    radiometer, photometer.-   Leaf area: 5.1 cm² measured with a leaf areameter, LI-COR 3000.-   Carbon dioxide exchange, _(FCO2 area), =0.000959 μg s⁻¹ (rate:    0.0427 μmole cm⁻² s⁻¹).-   Differential carbon dioxide measurements with an InfraRed Gas    Analyser (IRGA)(Type Mk.3, The analytical Development Co. Limited).

As Spartina is a C₄ plant it is assumed limited by light also above theoptimal photon flux of 0.1667 μmole cm⁻² s⁻¹.

1) Determination based on photon flux and area:

-   actual photosynthesis=1/36× photon flux×area=0.0269 μmole glucose    s⁻¹-   Light respiration per area unit, R_(Larea)=5/6× actual    photosynthesis=0.0224 μmole glucose s⁻¹.-   Net photosynthesis_(area): actual photosynthesis−light    respiration=0.0045 μmole glucose s⁻¹.-   Gross water flux (g)=6× photon flux=1.14 g s⁻¹.-   The correct way to express the light respiration and the net    photosynthesis is in relation to the weight of the gross water flux,    as they both are expressions of carbon dioxide production/uptake,    which is related to the weght (volume) of water:-   Light respiration_(w.weight)=R_(larea)/gross water flux=0.01965    μmole s⁻¹.-   (light respiration rate per weight unit=0.0385 μmole g⁻¹s⁻)-   Light respiration rate per water weight unit is, as noted above,    constant: 5×6⁻⁴=0.0038 μmole g⁻¹ s⁻¹

Conclusion: The measured value and the theortical value for lightrespiration rate are in good correlation.

Determinations based on carbon dioxide exchange measurement:

Measured net photosynthetic rate; F_(CO2)area=1.88 mg CO₂ s⁻¹ divided bythe mole weight of CO₂ (44 g) divided by the area (5.1 cm²) 0.0084 μmoleCO₂ cm⁻² s⁻¹. Net photosynthetic rate determined by photon flux/areadetermination (see above)=0.0088 μmole CO₂ cm⁻² s⁻¹.

The determination of the net phototsynthesis by the new method and bythe old method are practically identical.

Light Respiration:

-   The light respiration based on area (cm²): 1/36(photon flux    −F*_(CO2))×area.-   The light respiration based on gross water flux (g or cm³): 1/216    (1−F*_(CO2)/photon flux)×area.-   (* F_(CO2) is the net photosynthetic rate measured as CO₂ exchange).

Light respiration related to area based on a method which combines lightphoton flux and carbon dioxide exchange in a method related to area:1/36(0.1900−0.0427)×5.1=0.0263 μmole glucose s ⁻¹.

The result solely based on the new light flux/area method:

Light respiration per area unit, R_(Larea=)5/6× actualphotosynthesis=0.0224 μmole glucose s⁻¹

The results from the two methods are very alike.

Conclusion: The far easier photon flux method leads in this example toresults, which are comparable to the carbon dioxide exchange method.Furthermore it is possible to combine the two methods with a very goodresult.

Example 3 Determination of the Maximal Possible Harvest Per Hectare PerYear

The maximal net photosynthetic=The maximal net photosynthetic rate isone sixth of the actual photosynthetic rate at the optimal photon flux:1/6×1/36×1/6 μmole glucose cm⁻² s⁻¹. The weight of one mole of glucoseis 180 g. One year is assumed to consist of 365 days with 12 hours ofsunshine per day, with the optimum photon flux of 1/6 μmole cm⁻²s⁻¹=1667 μmole m⁻² s⁻¹.

The maximum net photosynthethis per hectare per year will under theabove assumptions be: (1/6)⁴ μmole glucose cm⁻² s⁻¹×180 g/mole×10⁸ cm⁻²ha⁻¹×60×60 12×365 s year⁻¹=6000 kg m⁻² year⁻¹ or 60 tons of carbohydrateper hectare per year.

This result is of the same order of magnitude as the potential netphotosynthesis per year in the tropics of 24-26 g m⁻² day⁻=88-95 tonsper hectare per year according to Mc Gregor and Niewolt (Tropicalclimatology, John Whiley and Sons, 1998).

In Schleswig Holstein (Germany) the harwest of wheat (year 2000) isabout 10 ton per hectare per year. The daily average of sunshine is 4.2hours in Schleswig Holstein according to Ridder (Klimaregionen und typenin Nordwestdeutschland, Verlagsanstalt Heinr. & J. Lechte, Emsdetten inWestf. 1935). This average of 4.2 hours will, taken over a year, give amaximum possible net photosynthetic production of 21 tons per hectareper year. When those 21 tons per year are compared to the actual grainharvest of 10 tons of wheat grain per hectare per year, to which strawand underground biomass (roots) should be added, one is likely to bevery close to the maximal harvest possible. A detailed study includingstraw and root biomass plus a precise registration of the light photonflux over a year will give a precise idea of whether an improvement ofplant breeds, genetic engineering, fertilizer treatment or the likecould improve the harvest.

1. A method for determination of the actual photosynthetic rate (thegross photosynthesis) of plants, wherein: the light photon flux fallingon the photosynthetising surface area of the leaves is measured andconverted directly to the amount of glucose produced per unit of thephotosynthetising area of the plant or the plant area per unit of timeby means of the conversion factor 1/36, as it requires 36 photons toproduce one molecule of glucose and light is related to the plantsurface area, the total actual photosynthesis of the plant, the plantpart or the plant area is calculated by multiplying the actualphotosynthetic rate by the size of the area, and optionally the lightrespiration rate of plants is determined by multiplying the total actualphotosynthesis by the conversion factor 5/6, as 5/6 of the amount of CO₂necessary for the actual photosynthesis rate is produced by the lightrespiration.
 2. A device for use in the method according to claim 1,enabling a direct determination of the actual photosynthetic rate (thegross photosynthesis) of plants by measuring the light photon fluxfalling on the photosynthetising surface area of the leaves andconverting said flux to the specific amount of glucose produced per unitof the photosynthetising area of the plant or the plant area per unit oftime, said device cornprising one or more photon fluxmeter(s) and anareameter connected to a computer unit which, based on the measuredphoton flux, can calculate and read out the total actual photosynthesisof the plant, the plant part or the plant area and, if desired, thelight respiration rate of the plant area in question.
 3. Use of themethod according to claim 1 for the determination and evaluation of anyprocess related to the actual photosynthesis, including plant growth,net photosynthesis, plant respiration in light, gross and net waterflux, CO₂ uptake and oxygen emisslon.
 4. Use of the method according toclaim 1 for the evaluation of the growth of plants and algae, the actualphotosynthesis and the light respiration based on a direct measurementof the light photon flux and the plant surface area and conversion ofthe measurement results to uptake and emission of CO₂, O₂ and H₂O inmarine and fresh water environments.
 5. Use of the method according toclaim 1 for agricultural and forestal evaluation of any process relatedto the actual photosynthesis, including plant growth, netphotosynthesis, plant respiration in light, gross and net water flux,CO₂ uptake and oxygen emission.
 6. Use of the method according to claim1 for the evaluation of the growth of plants and algae and foragricultural and forestal evaluation of any process related to theactual photosynthesis, including plant growth, net photosynthesis, plantrespiration in light, gross and net water flux, CO₂ uptake and oxygenemission, where the measurements are carried out from a satellite or anaeroplane.
 7. Use of the method according to claim 1 in an apparatus orin computers or computer programs of any kind for the evaluation of thegrowth of plants and algae and for agricultural and forestal evaluationin relation to the actual photosynthesis, including plant growth, netphotosynthesis, plant respiration in light, gross and net water flux,CO₂ uptake and oxygen emission.
 8. Use of the device according to claim2, where the measurements are carried out from a satellite or anaeroplane.